The present invention relates to a variable magnification arrangement and more particularly, to a variable magnification device provided with a plurality of interchangeable projection lenses of different focal lengths for use, for example, in printing and reading apparatuses and the like employing microfiche films.
Commonly, microfiche films which are one type of microfilms widely employed for recording documents, office papers, etc., have various contraction rates mainly of 1/24, 1/48 and 1/42. Therefore, if a reading and printing apparatus for reading or copying such microfiche films is provided with only one projection lens having a predetermined focal length, the enlarged image to be projected is inevitably limited in size.
Accordingly, in the conventional reading and printing apparatuses, the arrangement has been such as to interchange in each case projection lenses having focal lengths (projection magnification) corresponding to the contraction rates of the microfiche films. The known arrangement as described above, however, has such disadvantages that not only storage is required for such interchangeable projection lenses, but interchanging thereof is troublesome requiring time, while focusing adjustment is necessary each time there is an interchange. Meanwhile, there has also been conventionally proposed an arrangement in which the projection lenses as described above are incorporated in the reading and printing apparatus for selectively bringing the projection lenses the desired focal length into the projecting position, which arrangement, however, is also disadvantageous in that because of the considerable space required, the apparatus tends to be large in size, while focusing adjustment of the projection lens is extremely difficult, since such lenses are disposed in the inner portion of the apparatus.
In order to overcome the disadvantages as described above, there has further been proposed another known variable magnification device, for example, in U.S. Pat. No. 3,713,737 or in Japanese Utility Model Laid-Open publication No. 51/52252 wherein a plurality of projection lenses having different focal lengths are adapted to move as one unit for bringing a particular projection lens suitable for the purpose over the projecting position for focusing adjustment thereof by one focusing adjusting means provided at said projecting position. The known arrangement as described above still has such drawbacks that during change-over of the desired projection lens to the projecting position, displacement of the focal point inevitably takes place due to rotation of the projection lens through rotational resistance between a toothed portion of the focusing adjusting means and that of the projection lens, thus requiring the focusing adjustment at each change-over of the projection lenses. Furthermore, in the arrangement as described above, if the focusing adjusting means is inadvertently touched by an operator, deviation or displacement of the focal point may occur, also requiring readjustment.
Another disadvantage inherent in the known arrangements is that since focal lengths, f number and projection magnification differ according to the projection lenses employed, intensity of illumination of the projected images tend to be different, for example, in a reading and printing apparatus at an observation screen for reading and at an exposure station for printing when such projection lenses are merely changed over to the projecting position, and thus an exposure adjustment is required each time the projection lenses are interchanged for obtaining copied images of optimum density at all times.
Accordingly, an essential object of the present invention is to provide a variable magnification device for use in various apparatuses and equipment employing a plurality of interchangeable lenses, for example, in a reading and printing apparatus in which focusing adjustment is readily effected without necessity for re-adjustment at the time of each projection lens change-over, with substantial elimination of the disadvantages inherent in the conventional variable magnification devices of this kind.
Another important object of the present invention is to provide a variable magnification device of the above described type which is equipped with focusing adjusting means adapted to be moved to engage the projection lens during the focusing adjusting for adjusting the focusing only of the projection lens which has been changed over to the projecting position, while the focusing adjusting means is arranged to be normally isolated from the projection lens so that the projection lens once adjusted for focusing is not moved from the focused position despite further change-over, so that the necessity of readjustment at such change-over is eliminated.
A further object of the present invention is to provide a variable magnification device of the above described type in which exposure adjustment through control of intensity of illumination of projected images is simultaneously effected with the focusing adjustment in association with the changeover of a change-over plate for the projection lenses.
A still further object of the present invention is to provide a variable magnification device of the above described type which has a simple construction and is stable in functioning without the possibility of malfunction, and can be incorporated at low cost into various apparatuses and equipment employing a plurality of interchangeable lenses for changing-over.